Aqueous liquids are injected into the earth and/or recovered from the earth during subterranean hydrocarbon recovery processes such as hydraulic fracturing (fracking) and tertiary oil recovery. In one or more such processes, an aqueous liquid called an “injectate” is injected into a subterranean formation. Injectates include water and entrained solids and/or solvents therein. In one or more such processes a water source called “produced water” is recovered, i.e. flows back from the subterranean formation and is collected. Produced water includes one or more of injectate, connate (native water present in the subterranean formation along with the hydrocarbon), sea water, and minor (<50 wt %) amounts of hydrocarbon products, which are hydrocarbon liquids or solids entrained (dispersed, emulsified, or dissolved) in the produced water. In some embodiments, one or more of the injectate and the produced water includes “corrodents” such as salts and/or other dissolved solids, liquids, or gasses that cause, accelerate, or promote corrosion of metal containments such as metal pipelines used to transport the water sources toward, into, out of, or away from a subterranean formation, metal tanks used to hold the water sources for a period of time, and/or other metal equipment or devices that contact the water sources before, during, or after injection or production. Non-limiting examples of such corrodents are carbon dioxide, oxygen, sodium chloride, calcium chloride, and/or sulfur dioxide.
Almost all operators in the oil and gas industry employ corrosion inhibitors to reduce internal corrosion in metal containments which are contacted by aqueous liquids containing corrodents. Corrosion inhibitors are added to the liquids and dissolved gasses which come into contact with metal surfaces where they act to prevent, retard, delay, reverse, and/or otherwise inhibit the corrosion of metal surfaces such as carbon-steel metal surfaces. In some cases one or more corrosion inhibitors are added to a water source, such as an injectate and/or a produced water; optionally, other additives such as polymers, surfactants, scale inhibitors, paraffin inhibitors, metal complexing agents, and the like are added along with the corrosion inhibitor or are present in the water source to which the corrosion inhibitor is applied. Such corrosion inhibitors are beneficial in that they permit the use of carbon steel components rather than the much more expensive high nickel, cobalt, and chromium alloys or other materials either more expensive than carbon steel and/or which inherently entail other disadvantages in suitability for the purpose of liquid containment.
One useful class of corrosion inhibitors commonly employed in water sources arising from oil recovery processes are sulfur-based corrosion inhibitors (sCI). Such sCI include, for example, thioglycolic acid, mercaptoethanol, and sodium thiosulfate. sCI are known to be highly effective corrosion inhibitors and are favored in the industry because they are also inexpensive. However, some sCI are known to produce hydrogen sulfide (H2S) gas when stored in an enclosed space for periods of time as short as 24 hours or even less at ambient temperatures such as about 20° C. This problem is exacerbated by storage of sCI concentrates, which have more than 1 wt % and as much as 90 wt % sCI in a solution of water, a water-miscible solvent, or a blend thereof. Conventional storage methods for sCI concentrates lead to substantial amounts of H2S gas buildup in the headspace of the containers holding such concentrates: in some embodiments, as much as 1000 ppm to 10,000 ppm H2S gas accumulates in the headspace of storage containers holding an sCI or sCI concentrate.
Hydrogen sulfide itself is a known corrodent recognized to cause severe corrosion issues in metal containments related to oil recovery operations. Hydrogen sulfide is toxic and dissolves in both hydrocarbon (oil/gasoline) and water streams. Further, where H2S is dissolved in such liquid streams it is also present as a flammable gas over the liquid streams, providing a severe health and safety risk.
The industry has recognized the hazards associated with H2S and has responded by development of H2S scavengers, which do not prevent degradation of sCI but rather adsorb or react with H2S to remove (scavenge) it from the systems where it becomes entrained. For example, triazines are known H2S scavengers. The scavenger approach is effective for eliminating naturally arising sources of H2S, such as in natural gas, produced water, and the like. However, once a molecule of sCI is degraded to release H2S, the residue of the degraded sCI is no longer effective as a corrosion inhibitor.
Consequently, there is a need in the industry to prevent accumulation of H2S gas during storage of sCI compounds and compositions containing sCI compounds. There is a need in the industry for stabilized sCI compositions. There is a need in the industry to improve the efficacy of corrosion inhibition compositions.